This invention relates to compression methods for wireless communication.
Session Initiation Protocol (SIP) is the protocol used for call control in the third generation mobile network starting from the Third Generation Partnership Project (3GPP) release 5. SIP uses textual encoding, which makes it easier to build services based on SIP, design extensions to SIP and debug the protocol. However, the textual encoding of SIP also has a serious drawback; it is well known that SIP messages are considerably larger than those of the protocols used for instance in Global System for Mobile communication (GSM) call control. Large message sizes result in increased call setup delay because more data needs to be transmitted over the low-bandwidth radio interface. This observation created a need to develop a solution which could reduce the call setup time. One such solution is the Signaling Compression (SigComp) protocol designed by the Internet Engineering Task Force (IETF). SigComp provides a framework for the compression of application-layer signaling between two network elements. The central piece of SigComp architecture is the Universal Decompressor Virtual Machine (UDVM), which is a virtual machine optimized for running decompression algorithms. Because of the UDVM, SigComp can support a wide range of compression algorithms instead of dictating a single algorithm to be supported by all SigComp endpoints.
SigComp is a mandatory part of the 3GPP release 5 IP Multimedia Subsystem (IMS). It is applied over the interface between a terminal and Proxy Call Session Control Function (P-CSCF), which is the first contact point for the terminal within the IMS. SigComp improves the quality of service the user perceives by reducing the idle time at call setup. It also allows the network to support a greater number of users by reducing the amount of resources consumed per subscriber.
The primary target for SigComp is cellular systems, where the mobile terminals have varying capabilities and undetected errors may be introduced on the cellular link. SigComp also addresses communication links with limited throughput, including cellular systems.